Free or paid?
Be patient in any case....consider that there is a spike in the number of book submittals right now, and things my take longer than before, etc.
Keep checking the store and watch your email for any notices.
Good luck w/your book(s).
My guess is that Apple has an agreement with the Publishers currently showing in the iTunes Textbook area to have their material shown for a specified period of time before other content shows up there.
With that being said, there are other iBook Author submissions located in various places in the iTunes store.